app_voicemail: Add the ability to specify multiple email addresses.

ASTERISK-24045
Reported by: Jacob Barber
Review: https://reviewboard.asterisk.org/r/3833/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@420577 f38db490-d61c-443f-a65b-d21fe96a405b
Fix build in devmode.

git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@420592 f38db490-d61c-443f-a65b-d21fe96a405b